1. Field of the Invention
This invention relates to an improved ball valve used in lethal gas or fluid service. Valves of this type are used in handling toxic gases such as phosgene used in the petrochemical industry.
Phosgene and similar toxic gases used in industrial applications must be handled with extreme caution as a concentration of as little as 50 parts per million can cause death in a matter of minutes. Typical valves used in this type of service include a body with a through bore with a ball positioned in the valve body bore. The ball has a through bore and controls fluid flow between the inlet connection and the outlet connection of the finished valve. A pair of seal elements commonly referred to as "seats" are located on each side of the ball and form a seal between the ball and valve body. Each seat has a spherical surface to seal against the ball's spherical outer surface. The seats in turn seal against the valve body with elastomeric seal elements or by grinding a sufficiently fine finish on the seat and corresponding valve body surface to effect a seal. Usually some type of preloading means such as a spring or belleville washer is used to initially preload the seal between the ball and the seats.
The opening and closing of the valve are controlled by a stem that engages a slot machined in the ball. The stem extends through a port machined in the valve body that is generally perpendicular to the valve bore. This port is sealed by a sleeve referred to as a "bonnet" that typically is bolted to the valve body. The stem is rotatable within the bonnet to open and close the valve. The annular space between the stern and bonnet is usually sealed with an elastomeric or advanced polymer plastic material. This seal element must be impervious to the lethal gas or fluid being handled while having sufficient elasticity to reliably seal between the stem and bonnet. Typical valves to date have relied upon a pair of seal elements with a monitoring port above the first seal element to detect when this seal element has deteriorated to the point where it no longer can seal between the stem and bonnet and contain the lethal gas or fluid. It is the type of valve that must reliably seal these legal gases or fluids to which the present invention is directed.
Additionally, the typical valve available to date has offered only advanced polymer plastic material seals, referred to as "polymerics" in the industry, for this critical stem to bonnet seal. When a seal begins leaking and the valve then becomes unreliable and unsafe, the solution has been to stop production while a new valve is installed. This results in lost production and a concomitant loss of revenue. The improved ball valve for use in lethal gas or fluid service of the current invention offers a substantial improvement by offering a reliable valve with a ceramic primary seal and redundant seals to ensure long service.
2. Description of Related Art
No valve offering the features of the improved ball valve of the present invention has been found.